The invention relates to an electrically operated fluid pump, in particular a coolant pump for the coolant system/heating system of a motor vehicle, with a stator and with a rotor, separated from the stator by a pipe, that is immersed in the coolant and carries a vane wheel.
The principle of separating the stator and rotor by a pipe, which makes it possible to dispose the rotor immersed in the coolant, is known from German Patent DE 3 702 028 C2.
A more-detailed description of such a pump can be found in German Patent Disclosure DE 44 11 960 A1. The pump shown in this reference has a bell-shaped rotor, whose cylindrical interior is engaged by the stator. A tubular or cup-shaped wall extends between the rotor and the stator, and a shaft about which the rotor is suspended rotatably is let into the bottom of the cup.
The anchoring of the shaft extends to only a slight depth into the interior of the cylindrical hollow chamber, because the space in this chamber is needed virtually entirely for accommodating the stator. The cylindrical wall between the stator and the rotor is quite thin, so that the gap width will be only slight and thus magnetic circuit losses will be slight. This impairs the stability of the suspension of the rotor.
A printed circuit board with a commutation circuit for the power supply to the stator can be disposed only in the axial extension of the stator and thus increases the installation depth of the pump.
The present invention on the one hand creates a coolant pump of reduced installation depth. On the other, it creates a coolant pump which while using little material enables stable support of the rotor and thus effectively limits disruptions in synchronism that might be caused by unavoidable imbalances, and which furthermore minimizes losses of efficiency resulting from friction between the rotor and the coolant in which it is immersed.
The short structural length is attained by using a claw pole stator as the stator for the pump of the invention.
The stable support and the reduction of friction losses are attained by disposing the rotor radially inside the stator. While in the known coolant pump, friction with the coolant can occur both on the inside of the rotor between the rotor and the pipe surrounding the stator and on the outside between the rotor and the surrounding housing, when the rotor is shifted into the interior of the stator, there is only an interstice, namely the space between the rotor and the pipe that separates the rotor from the stator. By this provision alone, friction losses are already reduced. A further factor that contributes to minimizing friction losses is that with the same radial dimensions of the motor, the diameter of the pipe can be kept less, when the rotor is on the inside. Thus for the same rpm, the path velocity of the rotor on its outer circumference is reduced, and as a consequence the friction is also less than in the conventional construction with the rotor on the outside.
The rotor located on the inside also has a reduced moment of inertia and can therefore be accelerated faster, and with less of a load on the electronic switches of its power supply circuit, than is possible with a rotor located on the outside. The reduced moment of inertia naturally leads to a reduced imbalance as well.
Shifting the stator to the outer circumference of the rotor also makes it possible for the shaft on which the rotor revolves to be lengthened, so that the center of gravity of the rotor comes to be located inside the shaft. The tilting moments that are exerted by an imbalance of the rotor on the mounts of the shaft are reduced thereby, so that overall, a lesser material thickness of the mounts suffices to anchor the rotor securely.
To keep the moment of inertia of the rotor slight and nevertheless achieve stable support, it is proposed that along with its permanent magnetic outer cylinder, the rotor should have a bearing shaft surround the shaft, which bearing shaft is spaced apart from the rotor by an empty annular chamber. This annular chamber can be open on its side remote from the vane wheel of the rotor.
The rotor is preferably made in one piece of a plastic-bonded magnetic material.
Further characteristics and advantages of the invention will become apparent from the ensuing description of exemplary embodiments with reference to the drawings.